Hermetic encapsulation of semiconductor devices is one of the most important steps in device manufacturing process for high reliability performance.
At the present time, the most widely used technique is electric-welding. The process is aimed at providing rugged and airtight seals between metallized ceramic and a metal lid (or cap).
A metal part (lid) is usually brazed onto a metal flange attached to a ceramic sleeve. This is done in a high temperature environment. The seal is accomplished by electric-welding the metal flange onto the metal lid.
It is noted that the existence of a "shoulder-out" portion of the metal flange is essential in order to perform the electric-welding; i.e., to provide the path of welding current.
However, in most microwave applications, the extended shoulder is very undesirable. The metal flange causes extreme mismatch problems between the semiconductor devices and the associated circuits. In many instances, the flange "shoulder" of individual packages must be trimmed off mechanically.
The present semiconductor package encapsulation process is essentially one of "cold" hermetic sealing. There is no "shoulder-out" or heat-induced problem in the process. The process employs two major features. The first feature is the utilization of a two step structure of the dielectric sleeve. The second is the electroforming (deposition) over the metal lid and ceramic metallization.
The present invention is hereinafter referred to as the electroplated microwave package encapsulation process. There are a multiplicity of advantages of this process over the prior art. One of the advantages is that minimum package parasitics is achieved in microwave applications. Another is a high yield in hermeticity with a rugged mechanical bonding between the lid and the dielectric sleeve is obtained. Still another is that the sealing process does not involve any high temperature cycle. A further advantage is that independent of the package size, the sealing process is cost effective in large volume production.